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ASF GitHub Bot logged work on BEAM-7013: ---------------------------------------- Author: ASF GitHub Bot Created on: 31/Jul/19 05:58 Start Date: 31/Jul/19 05:58 Worklog Time Spent: 10m Work Description: robinyqiu commented on pull request #9144: [BEAM-7013] Integrating ZetaSketch's HLL++ algorithm with Beam URL: https://github.com/apache/beam/pull/9144#discussion_r309049344 ########## File path: sdks/java/extensions/zetasketch/src/main/java/org/apache/beam/sdk/extensions/zetasketch/HllCountMergePartialFn.java ########## @@ -0,0 +1,151 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you under the Apache License, Version 2.0 (the + * "License"); you may not use this file except in compliance + * with the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ +package org.apache.beam.sdk.extensions.zetasketch; + +import com.google.zetasketch.HyperLogLogPlusPlus; +import java.io.IOException; +import java.io.InputStream; +import java.io.OutputStream; +import javax.annotation.Nullable; +import org.apache.beam.sdk.coders.AtomicCoder; +import org.apache.beam.sdk.coders.Coder; +import org.apache.beam.sdk.coders.CoderRegistry; +import org.apache.beam.sdk.coders.NullableCoder; +import org.apache.beam.sdk.extensions.zetasketch.HllCountMergePartialFn.HyperLogLogPlusPlusWrapper; +import org.apache.beam.sdk.transforms.Combine; + +/** + * {@link Combine.CombineFn} for the {@link HllCount.MergePartial} combiner. + * + * @param <T> type of the HLL++ sketch to be merged + */ +class HllCountMergePartialFn<T> + extends Combine.CombineFn<byte[], HyperLogLogPlusPlusWrapper<T>, byte[]> { + + // Call HllCountMergePartialFn.create() to instantiate + private HllCountMergePartialFn() {} + + static HllCountMergePartialFn<?> create() { + return new HllCountMergePartialFn(); + } + + /** + * Accumulator for the {@link HllCount.MergePartial} combiner. Cannot use {@link + * HyperLogLogPlusPlus} directly because we need an "identity element" for the {@code merge} + * operation, and we are not able to create such "identity element" of type {@link + * HyperLogLogPlusPlus} without knowing the sketch precision and value type. + */ + static final class HyperLogLogPlusPlusWrapper<T> { + @Nullable private HyperLogLogPlusPlus<T> hll; + + private HyperLogLogPlusPlusWrapper(@Nullable HyperLogLogPlusPlus<T> hll) { + this.hll = hll; + } + } + + /** + * Coder for the {@link HyperLogLogPlusPlusWrapper} class with generic type parameter {@code T}. + */ + private static final class HyperLogLogPlusPlusWrapperCoder<T> + extends AtomicCoder<HyperLogLogPlusPlusWrapper<T>> { + + private static final HyperLogLogPlusPlusWrapperCoder<?> INSTANCE = + new HyperLogLogPlusPlusWrapperCoder<>(); + + private final Coder<HyperLogLogPlusPlus<T>> nullableHllCoder = + NullableCoder.of(HyperLogLogPlusPlusCoder.of()); + + // Generic singleton factory pattern; the coder works for all HyperLogLogPlusPlusWrapper objects + // at runtime regardless of type T + @SuppressWarnings("unchecked") + static <T> HyperLogLogPlusPlusWrapperCoder<T> of() { + return (HyperLogLogPlusPlusWrapperCoder<T>) INSTANCE; + } + + @Override + public void encode(HyperLogLogPlusPlusWrapper<T> value, OutputStream outStream) + throws IOException { + nullableHllCoder.encode(value.hll, outStream); + } + + @Override + public HyperLogLogPlusPlusWrapper<T> decode(InputStream inStream) throws IOException { + return new HyperLogLogPlusPlusWrapper<T>(nullableHllCoder.decode(inStream)); + } + + @Override + public void verifyDeterministic() throws NonDeterministicException { + nullableHllCoder.verifyDeterministic(); + } + } + + @Override + public Coder<HyperLogLogPlusPlusWrapper<T>> getAccumulatorCoder( + CoderRegistry registry, Coder<byte[]> inputCoder) { + return HyperLogLogPlusPlusWrapperCoder.of(); + } + + @Override + public HyperLogLogPlusPlusWrapper<T> createAccumulator() { + return new HyperLogLogPlusPlusWrapper<>(null); + } + + @Override + public HyperLogLogPlusPlusWrapper<T> addInput( + HyperLogLogPlusPlusWrapper<T> accumulator, byte[] input) { + if (accumulator.hll == null) { + @SuppressWarnings("unchecked") + HyperLogLogPlusPlus<T> hll = (HyperLogLogPlusPlus<T>) HyperLogLogPlusPlus.forProto(input); + accumulator.hll = hll; + } else { + accumulator.hll.merge(input); + } + return accumulator; + } + + @Override + public HyperLogLogPlusPlusWrapper<T> mergeAccumulators( + Iterable<HyperLogLogPlusPlusWrapper<T>> accumulators) { + HyperLogLogPlusPlusWrapper<T> merged = createAccumulator(); + for (HyperLogLogPlusPlusWrapper<T> accumulator : accumulators) { + if (accumulator.hll == null) { + continue; + } + if (merged.hll == null) { + // Cannot set merged.hll to accumulator.hll directly because we shouldn't mutate accumulator + @SuppressWarnings("unchecked") + HyperLogLogPlusPlus<T> hll = + (HyperLogLogPlusPlus<T>) + HyperLogLogPlusPlus.forProto(accumulator.hll.serializeToProto()); Review comment: Reason is mentioned in the comment above: `// Cannot set merged.hll to accumulator.hll directly because we shouldn't mutate accumulator` If you are asking for reasons why we shouldn't mutate `accumulator`, it is related to a design flaw in our `CombineFn` function. The result of that is, in short, people who are implementing `mergeAccumulators` need to comply with this instruction: https://github.com/apache/beam/blob/master/sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/Combine.java#L406 ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org Issue Time Tracking ------------------- Worklog Id: (was: 285518) Time Spent: 4h 10m (was: 4h) > A new count distinct transform based on BigQuery compatible HyperLogLog++ > implementation > ---------------------------------------------------------------------------------------- > > Key: BEAM-7013 > URL: https://issues.apache.org/jira/browse/BEAM-7013 > Project: Beam > Issue Type: New Feature > Components: extensions-java-sketching, sdk-java-core > Reporter: Yueyang Qiu > Assignee: Yueyang Qiu > Priority: Major > Fix For: 2.16.0 > > Time Spent: 4h 10m > Remaining Estimate: 0h > -- This message was sent by Atlassian JIRA (v7.6.14#76016)